summaryrefslogtreecommitdiffstats
path: root/lib/jhash.c
diff options
context:
space:
mode:
Diffstat (limited to 'lib/jhash.c')
-rw-r--r--lib/jhash.c187
1 files changed, 187 insertions, 0 deletions
diff --git a/lib/jhash.c b/lib/jhash.c
new file mode 100644
index 0000000..0d561ef
--- /dev/null
+++ b/lib/jhash.c
@@ -0,0 +1,187 @@
+/* jhash.h: Jenkins hash support.
+ *
+ * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
+ *
+ * http://burtleburtle.net/bob/hash/
+ *
+ * These are the credits from Bob's sources:
+ *
+ * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
+ * hash(), hash2(), hash3, and mix() are externally useful functions.
+ * Routines to test the hash are included if SELF_TEST is defined.
+ * You can use this free for any purpose. It has no warranty.
+ *
+ * Copyright (C) 2003 David S. Miller (davem@redhat.com)
+ *
+ * I've modified Bob's hash to be useful in the Linux kernel, and
+ * any bugs present are surely my fault. -DaveM
+ */
+
+#include "zebra.h"
+#include "jhash.h"
+
+/* The golden ration: an arbitrary value */
+#define JHASH_GOLDEN_RATIO 0x9e3779b9
+
+/* NOTE: Arguments are modified. */
+#define __jhash_mix(a, b, c) \
+ { \
+ a -= b; \
+ a -= c; \
+ a ^= (c >> 13); \
+ b -= c; \
+ b -= a; \
+ b ^= (a << 8); \
+ c -= a; \
+ c -= b; \
+ c ^= (b >> 13); \
+ a -= b; \
+ a -= c; \
+ a ^= (c >> 12); \
+ b -= c; \
+ b -= a; \
+ b ^= (a << 16); \
+ c -= a; \
+ c -= b; \
+ c ^= (b >> 5); \
+ a -= b; \
+ a -= c; \
+ a ^= (c >> 3); \
+ b -= c; \
+ b -= a; \
+ b ^= (a << 10); \
+ c -= a; \
+ c -= b; \
+ c ^= (b >> 15); \
+ }
+
+/* The most generic version, hashes an arbitrary sequence
+ * of bytes. No alignment or length assumptions are made about
+ * the input key.
+ */
+uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
+{
+ uint32_t a, b, c, len;
+ const uint8_t *k = key;
+
+ len = length;
+ a = b = JHASH_GOLDEN_RATIO;
+ c = initval;
+
+ while (len >= 12) {
+ a += (k[0] + ((uint32_t)k[1] << 8) + ((uint32_t)k[2] << 16)
+ + ((uint32_t)k[3] << 24));
+ b += (k[4] + ((uint32_t)k[5] << 8) + ((uint32_t)k[6] << 16)
+ + ((uint32_t)k[7] << 24));
+ c += (k[8] + ((uint32_t)k[9] << 8) + ((uint32_t)k[10] << 16)
+ + ((uint32_t)k[11] << 24));
+
+ __jhash_mix(a, b, c);
+
+ k += 12;
+ len -= 12;
+ }
+
+ c += length;
+ switch (len) {
+ case 11:
+ c += ((uint32_t)k[10] << 24);
+ /* fallthru */
+ case 10:
+ c += ((uint32_t)k[9] << 16);
+ /* fallthru */
+ case 9:
+ c += ((uint32_t)k[8] << 8);
+ /* fallthru */
+ case 8:
+ b += ((uint32_t)k[7] << 24);
+ /* fallthru */
+ case 7:
+ b += ((uint32_t)k[6] << 16);
+ /* fallthru */
+ case 6:
+ b += ((uint32_t)k[5] << 8);
+ /* fallthru */
+ case 5:
+ b += k[4];
+ /* fallthru */
+ case 4:
+ a += ((uint32_t)k[3] << 24);
+ /* fallthru */
+ case 3:
+ a += ((uint32_t)k[2] << 16);
+ /* fallthru */
+ case 2:
+ a += ((uint32_t)k[1] << 8);
+ /* fallthru */
+ case 1:
+ a += k[0];
+ }
+
+ __jhash_mix(a, b, c);
+
+ return c;
+}
+
+/* A special optimized version that handles 1 or more of uint32_ts.
+ * The length parameter here is the number of uint32_ts in the key.
+ */
+uint32_t jhash2(const uint32_t *k, uint32_t length, uint32_t initval)
+{
+ uint32_t a, b, c, len;
+
+ a = b = JHASH_GOLDEN_RATIO;
+ c = initval;
+ len = length;
+
+ while (len >= 3) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ __jhash_mix(a, b, c);
+ k += 3;
+ len -= 3;
+ }
+
+ c += length * 4;
+
+ switch (len) {
+ case 2:
+ b += k[1];
+ /* fallthru */
+ case 1:
+ a += k[0];
+ }
+
+ __jhash_mix(a, b, c);
+
+ return c;
+}
+
+
+/* A special ultra-optimized versions that knows they are hashing exactly
+ * 3, 2 or 1 word(s).
+ *
+ * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
+ * done at the end is not done here.
+ */
+uint32_t jhash_3words(uint32_t a, uint32_t b, uint32_t c, uint32_t initval)
+{
+ a += JHASH_GOLDEN_RATIO;
+ b += JHASH_GOLDEN_RATIO;
+ c += initval;
+
+ __jhash_mix(a, b, c);
+
+ return c;
+}
+
+uint32_t jhash_2words(uint32_t a, uint32_t b, uint32_t initval)
+{
+ return jhash_3words(a, b, 0, initval);
+}
+
+uint32_t jhash_1word(uint32_t a, uint32_t initval)
+{
+ return jhash_3words(a, 0, 0, initval);
+}